When a gas generating agent is used in an inflator for use in a safety apparatus for a vehicle such as a airbag apparatus disposed in a vehicle, it is very important to improve ignition ability of the gas generating agent in order to ensure product reliability.
And, it is important to decrease the combustion temperature of the gas generating agent because the heat load on the coolant disposed in the inflator can be reduced and an amount of a coolant can be decreased.
However, where the combustion temperature of the gas generating agent is decreased too much, the ignition ability is degraded. Therefore, it is desirable to decrease the combustion temperature and obtain excellent ignition ability at the same time.
A stable force to deploy a bag is required in inflators for airbag apparatuses, but a burning rate of a gas generating agent which burns inside an inflator is known to change in a range of a power of the pressure index n according to the following formula under the effect of pressure change inside the inflator:r=aPn (where r is a burning rate, a is a constant (a value inherent to the gas generating composition), P is a pressure inside the inflator, and n is a pressure index (a value inherent to the gas generating composition)).
Where a gas generating agent has a large index n, a burning rate of the gas generating agent changes significantly because of pressure change inside the inflator, thereby also causing a significant change in an amount of gas generated by the combustion of the gas generating agent.
In such a case, the deployment force of an air bag changes due to pressure change inside the inflator and the air bag fails to act as a protection device.
Therefore, it is important to provide a gas generating agent with a small index n and provide a gas generating agent having combustion stability that is not affected significantly by changes in an environment, such as temperature and pressure.
JP-B No. 3907548 discloses a gas generating composition for an inflator including: (a) melamine cyanurate or a mixture of melamine cyanurate and a nitrogen-containing organic compound as a fuel, and (b) an oxygen-containing oxidizing agent, which can exhibit a specific effect such as a low combustion temperature and a small amount of generated hazardous gas, as a result of using novel melamine cyanurate as a fuel component.
It is described that the compounding ratio (mass ratio), nitrogen-containing organic compound/melamine cyanurate, in the mixture of melamine cyanurate and nitrogen-containing organic compound, is preferably 0.05 to 8, more preferably 0.1 to 6, and even more preferably 0.2 to 2.
Decreasing combustion temperature is described as a problem to be solved, but improving ignition ability is not a problem to be solved, and it is only described that the ignition ability is improved by selecting an appropriate binder.
And the value of the pressure index is given as 0.23 in Example 28 and 0.31 in Example 29 in Table 4.